1. Field of the Invention
The present invention relates to the stator arrangement of an alternator driven by an internal combustion engine for a vehicle such as a passenger car, a truck, or a boat.
2. Description of the Related Art
Recently, the number various devices in a vehicle such as safety devices has increased, and thus, the output power of alternators is required to be increased. This also involves an increase in the heat radiation of alternators.
PCT Pat. application 92/06527 discloses a sample of a high power alternator. In this application, U-shaped conductor segments are inserted into slots of the stator core from one end and are welded with one another to form a stator winding. Because the U-shaped conductor segments can be disposed regularly, a high conductor occupation ratio can be provided, thereby increasing the output power.
Another structure for improving the cooling effect of the stator winding is disclosed in JP-U-1-27406. The coil ends of the stator winding is formed flat to increase the surface area of winding to be cooled
In these conventional structures, two coil-end groups have the same shape and the same size, and there is no difference in the heat radiation. Because the amount of the cooling air sent to two coil-end groups is different, there is a difference in temperature between two coil-end groups.
For example, in an alternator having a pulley at the front thereof and a rectifier at the rear thereof, the heat of the rectifier heats the cooling air sent to the rear-side coil-end group, causing the temperature of the coil-end group higher than the other.
Moreover, the rear side of the alternator faces an engine and is heated thereby. Thus, the temperature of the cooling air supplied to the rear-side coil-end group may become high according to the location of the alternator in the engine compartment. As a result, the rear-side coil-end group can not be cooled and the temperature thereof become too high.
This causes a temperature rise of the stator winding with an undesirable difference in temperature between two coil-end groups. The temperature difference between two coil-end groups causes a difference in temperature between two housings. If this temperature difference becomes too big, the axis of the rotor may be shifted due to a difference in the thermal expansion thereof, thereby causing magnetic noise and vibration.